Disulfonate

Diazo coupling involves the N exocyclic atom of the diazonium salt, which acts as an electrophilic center. The diazonium salts of thiazoles couple with a-naphthol (605). 2-nitroresorcinol (606), pyrocatechol (607-609), 2.6-dihydroxy 4-methyl-5-cyanopyridine (610). and other heteroaromatic compounds (404. 611) (Scheme 188). The rates of coupling between 2-diazothicizolium salts and 2-naphthol-3.6-disulfonic acid were measured spectrophotometrically and found to be slower than that of 2-diazopyridinium salts but faster than that of benzene diazonium salts (561 i. The bis-diazonium salt of bis(2-amino-4-methylthiazole) couples with /3-naphthol to give 333 (Scheme 189) (612). The products obtained from the diazo coupling are usuallv highly colored (234. 338. 339. 613-616). 

Naphthol-3,6-disulfonic acid 9.0 to 9.5 Dark blue to light blue 4... 

Chromotropic acid (1,8-dihydroxy naphthalene- 3,6-disulfonic acid)[148-25-4... 

Technologically, the most important examples of such couplers are 1-naphthylamine, 1-naphthol, and sulfonic acid derivatives of 1-naphthol (Fig. 2). Of great importance in the dyestuff industry are derivatives of l-naphthol-3-sulfonic acid, such as H-acid (8-amino-l-naphthol-3,6-disulfonic acid [90-20-0])... 

Sulfonation. Fuming sulfuric acid reacts with coumarin to give coumarin-6-sulfonic acid [27279-86-3] at moderate temperature and coumarin-3,6-disulfonic acid [69089-38-9] at higher temperature. 

Naphthalene-3,6-disulfonic acid, l,8-dihydroxy-2-(2-thiazolylazo)-analytical uses, 6, 328 Naphthalenes... 

Lissamine Green B l-[bis-(4,4 -dimethylaminophenyl)methyl]-2-hydroxynapbthalene-3,6-disulfonic acid sodium salt. Acid Green 50 [3087-16-9] M 576.6, m >200°(dec). Cl... 

Modified PAN fibres containing aldehyde groups can be used to obtain chemically stained fibres. The chemical addition of dyes can be conducted following two schemes A) The fibres of the above composition are treated with aromatic amines, e.g., l-amino-8-hydroxynaphthalene-3,6-disulfonic acid ( H-acid ), and then azocoupling is carried out with a diazonium salt ... 

The rate constants in Figure 5-3 were measured by injecting the solution of the (E)-diazoate into a buffer solution that also contained a highly reactive coupling component (2-naphthol-3,6-disulfonic acid, except at pH values below 2.5, where l,8-dihydroxynaphthalene-3,6-disulfonic acid was used instead). The diazonium ion formed reacts rapidly with these naphthols, and the concentration of the corresponding azo compounds was determined spectrophotometrically. 

A quantitative study of the azo coupling reactions of heterocyclic diazo compounds was made by Sawaguchi et al. (1971), who measured the coupling rates of seventeen heterocyclic diazonium ions with R-acid (2-naphthol-3,6-disulfonic acid) and compared them with those of the benzenediazonium ion with the same coupling component. All the heterocyclic diazonium ions investigated react faster with R-acid than does the benzenediazonium salt. More recently, Diener and Zollinger (1986) confirmed Sawaguchi s results and interpreted them in more detail. 

The pK values for azolediazonium ions (Scheme 12-4) refer to the heterolysis of the NH bond, not to the addition of a hydroxy group. Therefore, these heteroaromatic diazo components may react either as a cation (as shown in Scheme 12-4) or as the zwitterion (after loss of the NH proton). Diener and Zollinger (1986) investigated the relative reactivities of these two equilibrium forms (Scheme 12-5) in the azo coupling reaction of l,3,4-triazole-2-diazonium ion with the tri-basic anion of 2-naphthol-3,6-disulfonic acid. 

Fig. 12-1. Correlation between azo coupling rates of substituted benzenediazonium ions with the 2-naph-thoxide-3,6-disulfonate trianion and the chemical shifts of protons at the position of the diazonio group in NMR spectra of the corresponding monosubstituted benzene parent compounds (Diener and Zollinger, 1986).

Zollinger (1971) calculated the actual rate constant referring to the monomeric diazo component from the (overall) measured rates and the dimerization equilibrium constant. The ratio of rates of the first to the second azo coupling reaction of the biphenyl-4,4 -bis-diazonium ion with the trianion of 2-naphthol-3,6-disulfonic acid at 15 °C, k /k2 9 is 80. 

Bagal et al. (1975) investigated in more detail the role of donor-acceptor complexes in the azo coupling reaction of the 4-nitrobenzenediazonium ion with 2-naphthylamine-3,6-disulfonic acid and that of the 4-chlorobenzenediazonium ion with 2-naphthol-6-sulfonic acid. Their kinetic results are, as would be expected, compatible with the mechanisms shown in Schemes 12-74 or 12-75. 

Micellar catalysis of azo coupling reactions was first studied by Poindexter and McKay (1972). They investigated the reaction of a 4-nitrobenzenediazonium salt with 2-naphthol-6-sulfonic and 2-naphthol-3,6-disulfonic acid in the presence of sodium dodecylsulfate or hexadecyltrimethylammonium bromide. With both the anionic and cationic additives an inhibition (up to 15-fold) was observed. This result was to be expected on the basis of the principles of micellar catalysis, since the charges of the two reacting species are opposite. This is due to the fact that either of the reagents will, for electrostatic reasons, be excluded from the micelle. 

Amaranth (E 123, Cl Food Red 9) is a mono azo dye, with the chemical name trisodium 3-hydroxy-4(4-sulfonato-l-naphtylazo)-2,7-naphthalenedisulfonate) (or trisodium 2-hydroxy-l-(4-sulfonato-l-napthylazo) naphthalene-3,6-disulfonate). The calcium and potassium salts are also permitted. Amaranth is a reddish-brown powder or granules, soluble in water, sparingly soluble in ethanol, with a maximum absorption in water at 520 nm (Ei " = 440). It has been banned in the US since 1976. " Amaranth can be used also as a dye for cosmetics, synthetic fibers, leather, papers, and some plastics. 

Ogura et a/.153 reduced C02 to methanol using the so-called Everitt s salt (K2Fe2+[Fe2+(CN)6])-modified electrode by a somewhat complicated but interesting route in the presence of a metal complex, such as Fe(II), Co(II), and Ni(II) complexes of 1-nitroso-2-naphthyl-3,6-disulfonic acid, and additional methanol ... 

The yellow ink jet dyes (and pigments) are metal-free azo dyes, such as Cl Direct Yellow 132 and Cl Acid Yellow 23 (Tartrazine).48,49 Most of the magentas are azo dyes derived from H-acid (l-amino-8-naphthol-3,6-disulfonic acid), such as (62), and xanthenes, such as Cl Acid Red 52 and Cl Acid Red 289.48,49 Where high lightfastness is a requirement, a copper complex azo dye, Cl Reactive Red 23 (63), is used. However, such dyes are dull (see Section 9.12.3.2). Nickel complex PAQ dyes, such as (22), are claimed to be brighter and to have similar high lightfastness... 

Several color reactions were reported for heterocycbc nitramines RDX and HMX [43, 44, 53, 58]. These nitramines release formaldehyde when treated with concentrated sulfuric acid. Therefore, the use of 1,8-dihhydroxynaphthalene-3,6-disulfonic acid (chromotropic acid) in concentrated sulfuric acid — a known reagent for the detection of formaldehyde [4] — produced the expected violet-pink color. The reaction is hardly specific other compounds that release formaldehyde under similar conditions will react in the same way. 

The completeness of coupling may be checked by the R-salt test as follows A few drops of the clear supernatant liquid is added to a small quantity of a solution of R-acid (jS-naphthol-3,6-disulfonic acid) in an excess of 2 TV sodium hydroxide. An intense red color is produced if unreacted diazonium salts are present. Obviously this test is satisfactory only if R-acid couples more rapidly with the diazonium salt than the coupling agent involved in the reactions and if the change to a red color is not obscured by other colors present in the reaction system.]... 

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